The present invention relates to a suspension for an oil conveying pipe or hose leading to a vessel.
In offshore oil loading it is common to transfer the oil to a vessel through a flexible metal pipe or rubber hoses. The terminations of these are relatively stiff, particularly for flexible metal pipes. Both the vessel and oil pipe are subjected to the forces of the sea, which in addition to variations in the pipe tension also give rise to variations in the fore and aft and athwartship angle between the pipe and its coupling to the vessel.
For oil transfer from the stern of a ship to the bow of another, or from a loading buoy to the bow of a ship, the variations in fore and aft angle are largest, and it has been common to suspend the coupling in the trunk part of a T-shaped pipe, the transverse part having been suspended in bearings on both sides. Here, a pipe swivel has been arranged on one or both sides of the transverse part, depending upon whether one or both of these parts have been carrying oil.
Oil carrying or conveying cardan joints have previously been used in mooring buoys for vessels, ref. U.S. Pat. Nos. 4,226,204, 4,309,955 and Norwegian patent 146897. These solutions have been developed in order to transfer mooring forces, which are much larger than the forces in the oil carrying pipe, and the design of the cardan joints employed reflects this fact. Furthermore, the geometric principles for routing the oil pipes through said cardan joints do not provide advantageous solutions for the suspension of an oil carrying pipe or hose to a vessel, not even if the basis for dimensioning the cardan joints were reduced to the hose tension at hand.
Vertical or approximately vertical oil carrying pipes from the sea floor or submerged buoys normally have a higher tension than those mentioned in the preceding paragraph, and hose tension is one of the most important criteria for determining whether or not the loading must be discontinued due to bad weather.
Measuring systems based on strain gauges and the like for hose tension have been included in the supporting structure for the coupling but it has been difficult to obtain sufficiently good measuring results since the suspension structure has been subjected to other factors than the hose tension. Furthermore, bending moments in the hose have also influenced the measurements. Bending moments in the hose have also caused additional loads in some of the claws in the coupling holding the hose coupler flange.
Therefore, it is very desirable to have freedom for the coupling to perform a pendulum movement in both the fore and aft and athwartship directions. The possibility to measure the hose tension is also of major importance. It has been suggested to use a ball joint suspension but the possible deflection angle may be too small for a ball joint suspension to be acceptable. Hose tension measurements can also be a problem when using ball joint suspensions. The object of the present invention is a suspension providing freedom for the coupling to adjust itself in the pipe pulling direction, such that no bending moment is transferred from the pipe to the coupling. Furthermore, one aims at measuring the pipe tension by means of elements included in the suspension.
This problem has been solved in that a 90.degree. pipe bend at one end is coupled to an oil carrying rotation swivel, that one or two plates are welded to the pipe wall at right angles to the swivel axis, that these plates have a cylindrical bore coaxially with the swivel, that a cylindrical load cell, also functioning as a shaft, is arranged in the bore, that this shaft and the oil carrying rotation swivel are suspended in and coupled to an existing pendulum suspension for an oil carrying pipe in such a manner that the two pendulum axes are perpendicular, thus forming an oil carrying cardan joint. The coupling is attached to the other end of the pipe bend, and it may be of advantage to arrange the point of application of the force in the load cell coaxially with the coupling.
The invention will be described below, reference being had to an advantageous embodiment, while concurrently indicating alternative embodiments of some of the components.